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 Posted: Wed Aug 01, 2012 9:44 am |
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Joined: Feb 07, 2010
Posts: 2718
Trade Rating: +6
Location: UK
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Update. I'm getting 5v from the map plug, any way to test the actual map sensor? It looked ok? If I unplug the map with engine running the car cuts out. If I leave it unplugged the engine hunts a bit, but runs fine.
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Posted: Wed Aug 01, 2012 11:15 am |
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Joined: Aug 01, 2011
Posts: 390
Trade Rating: 0
Location: Bath UK
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If you have an upstream O2 sensor going open circuit or short to earth ( which is what PP is telling you) then your fuel trims will go to max and trigger the P0170 fuel trim reached the set limit warning. So you need to investigate the open circuit or short to earth that it has found on the O2 sensor circuit. There may have been nothing wrong with the original O2 sensor and just changing it may not have cured the problem.
The best way to test a MAP sensor is to connect a hand vacuum pump with vacuum gauge and test its voltage output throughout the range. MAP sensor symptoms are driveability eg engine surging from low rpm pick up if it's causing rich mixture or if it's going the other way then weak mixture means poor acceleration especially uphill
First step for me would be to see what the actual long term and short term fuel trim figures are when the engine is running to see what the ECU is bitching about and when it's happening and compare that with the O2 readings at the time. O2 figures intermittently going wild? Then you still have an O2 sensor circuit problem
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Posted: Wed Aug 01, 2012 12:02 pm |
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Joined: Feb 07, 2010
Posts: 2718
Trade Rating: +6
Location: UK
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Thanks for the reply! I cant find the earth fault on the lambda, but then again the wires arnt conventional green for earth, red for live etc!
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Posted: Wed Aug 01, 2012 12:44 pm |
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Joined: Aug 01, 2011
Posts: 390
Trade Rating: 0
Location: Bath UK
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It's not an earth fault as such, P0131 tells you it's a short circuit to earth or open circuit so that's signal wire going to earth or losing contact
4 wire O2 sensor wiring
The black wire is almost always the O2 signal wire
Two same colour wires will be the O2 heater circuit (usually white)
The one remaining will be the earth.
If the signal wire shorts to earth that will also cause signal loss but much more common is a poor contact on the signal wire ( dramatic effects as the O2 puts out very low voltage of less than 1v) will cause intermittent open circuit.
Ideally you want to view your O2 sensor output whilst you drive and watch for any wierd readings, if your fuel trim goes sky high at the same point your O2 sensor goes beserk then you have found the fault and the reason for the P0170
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Posted: Wed Aug 01, 2012 1:44 pm |
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Joined: Feb 07, 2010
Posts: 2718
Trade Rating: +6
Location: UK
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Where might the poor contact be? In the Sensor, or the connector? Thanks for all the info. I cant get my pp2000 to give any outputs.
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Posted: Wed Aug 01, 2012 2:41 pm |
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Joined: Aug 01, 2011
Posts: 390
Trade Rating: 0
Location: Bath UK
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Very likely to be at the O2 connector (first one up from the sensor) as this gets most flexing and weather, even more likely is in the connectors if someone has put an aftermarket universal O2 sensor in there with inline crimp connectors, could be damaged/crushed/burnt wiring as the exhaust is close by or even poor contact up at the ECU.
Inspect the O2 connector very carefully for bad connection/ tarnishing
Do the codes reappear soon after clearing?
Are you able to view the O2 sensor output? It really is much easier to have a real time output trace to spot problems of this type
Are you able to view fuel trims?
With a 2004 car you are OBD2 so there's a load of software programs available where all you need to connect to a laptop is a usb to OBD2 interface
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Posted: Wed Aug 01, 2012 4:39 pm |
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Joined: Feb 07, 2010
Posts: 2718
Trade Rating: +6
Location: UK
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Ive managed to reset the codes tonight so il see how it goes. The wiring looked ok, it was all origonal wiring.
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Posted: Thu Aug 02, 2012 1:02 am |
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Joined: Aug 01, 2011
Posts: 390
Trade Rating: 0
Location: Bath UK
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OK see if the P0131 comes back up again as if it does then that will need attention first. If it's ok then it'll be worth doing a hard reset as Lee described earlier by disconnecting the battery for long enough and let the ECU reconfigure and relearn the best settings over again rather than just clearing fault codes which is kind of a soft reset. Always worth getting the ECU to do a relearn/recalibrate if you have changed or fixed something that affects normal engine running
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Posted: Wed Aug 08, 2012 2:58 pm |
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Joined: Feb 07, 2010
Posts: 2718
Trade Rating: +6
Location: UK
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Seems to be sorted now, fault has not come back in a week, so it was a faulty lambda!
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